The present invention relates to a method of effecting replication of data in a computer system.
In recent years, there has been demands for shortening the time which is required to make a copy of data stored in a storage owned by a corporation (hereafter, called a “backup”) and to store this backup copy in another storage. This is because, while the time required for backups is ever increasing in accordance with an increase in the amount of information owned by the corporation, the actual time assigned for such backups is being shortened due to the longer service hours of the corporation.
As a technique used to backup data stored in a storage without interrupting the daily operation of the corporation, a procedure called a snapshot has been proposed. A snapshot is a function in which a copy is made of the contents of a storage area in the storage at a particular moment without using a computer connected to the storage. With this function, the user uses an original storage area for business use and uses data stored in the copied storage area for a backup.
As a technique to enhance the scalability of a storage connected to a network, a cluster-structured storage system can be used. The cluster-structured storage system is based on a technique in which a conventional storage system, such as a disk array device, is regarded as one cluster, and a single storage system is constructed of a plurality of clusters.
So far, there are no documents in which execution of a snapshot in a cluster-structured storage system is suggested. Further, a simple combination of a cluster-structured storage system and a conventional snapshot technique merely results in a technique for copying storage areas within one cluster.
However, when copies of storage areas cannot be made between different clusters, there will exist a storage area to which another storage area can be copied and a storage area to which another storage area cannot be copied in one cluster-structured storage system, thereby ruining the scalability, which is the primary object of the cluster-structured storage system.
Further, if there are both a storage area from which data is copied and a storage area to which data is copied in the same cluster, the performance of such a cluster will not be improved. For example, when a storage area to which data is to be copied is created in the same cluster, an I/O of the operation is performed in the storage area from which data is copied and an online backup is made from the storage area to which data is copied, the cache memory contained in one cluster is shared by both the operation and the backup. Thus, the backup disturbs the normal I/O operation, which results in a delay in the operation. Further, if loads are concentrated on a particular cluster, the overall performance will also be deteriorated.